Clearance hole for self-piercing rivet

ABSTRACT

A system for attaching layers of material together comprised of a self-piercing rivet, a layer having a clearance hole through which the self-piercing rivet passes on assembly, and a layer free of a clearance hole and into which the self-piercing rivet is at least partially inserted. The system may include a third layer free of a clearance hole. The system may also include three layers wherein the clearance hole is formed in the middle layer. If the clearance hole is formed in the middle layer, the width of the hole may be greater than the diameter of the self-piercing rivet to avoid contact between the rivet and the middle layer. The layer having the clearance hole may be a hard material such as steel. One or more of the layers may be material that is difficult to pierce or can be damaged if pierced.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application which claims the prioritybenefit of co-pending U.S. Non-Provisional patent application Ser. No.14/736,595, filed Jun. 11, 2015 for “Clearance Hole For Self-PiercingRivet,” which claims the priority benefit of expired U.S. ProvisionalPatent Application Ser. No. 62/011,163, filed Jun. 12, 2014, the entiredisclosures of which, including the drawings, are hereby incorporated byreference.

TECHNICAL FIELD

The disclosed inventive concept relates generally to self-piercingriveting systems. More particularly, the disclosed inventive conceptrelates to a system for use with self-piercing rivets in which aclearance hole is formed in one of the layers prior to riveting.

BACKGROUND OF THE INVENTION

The automobile manufacturing industry is constantly faced with newchallenges in a wide array of areas including vehicle safety,reliability, durability and cost. Perhaps the greatest challenge facedby the automobile industry today is the need to improve fuel mileage toboth decrease carbon emissions and increase fuel economy for bothenvironmental and cost reasons, all without compromising safety, poweror durability. In 2011, new fuel economy requirements were imposed thatestablish a US vehicle fleet average of 54.5 miles per gallon by 2025.As the industry moves to that target year fuel annual economyrequirements will be ramped up for different-sized vehicles.

Efforts have been made to increase fuel economy for vehicles. Theseefforts can be divided into two approaches: the “supply” side and the“demand” side.

On the supply side attention is drawn to improving energy conversionefficiency through use of, for example, electric or hybrid-electricdrive trains. In addition, new vehicle drive trains, including smallerengines and more efficient transmission having multiple gears andtransfer cases, are being developed and employed. Other technologies,including start-stop and engine cylinder deactivation strategies, arealso proving effective at decreasing fuel consumption. Improvedtransmissions with multiple gears are also important elements toincreased fuel consumption efficiencies.

On the demand side weight reduction is key, though other aspects, suchas improved aerodynamics and drag reduction, are also important.Conventional vehicles, particularly trucks, rely on steel components.For over 100 years the material of choice for most vehicles is steel.Today steel makes up about 60% of the average car by weight.

Despite the improvement in steel composition the weight of steelregardless of type remains significant. It is also possible to reducevehicle weight when steel is used by reducing component thickness.However, at a certain point it is no longer practical to reduce steelthickness regardless of the steel grade used. The use of high strengthsteel or advanced, high strength steel does not improve the realizationthat there are limits to how much vehicle weight can be reduced by steelthickness reduction without compromising vehicle performance.

Thus as the automotive industry continues to focus on light weightingvehicles to meet customer expectations on fuel economy and CAFErequirements, interest in alternative materials including aluminumintensive vehicle applications has increased. This is because vehicleweight reduction is most directly accomplished through substitutinglighter materials for currently used steel parts. However, a limitedvariety of materials are available as a substitute for automotive steel.One such material is carbon fiber which is both lightweight and strong.

While carbon fiber offers certain performance advantages replacement ofthe steel body-in-white with carbon fiber is expensive and brings withit a relatively slow production process.

Accordingly, much attention is drawn to the use of aluminum which isabout ⅓ the weight of steel. Aluminum is not a new material forautomotive use and has been used as a material for castings for over 100years. The use of aluminum not only provides weight reduction but alsoresults in good crash performance. Research has shown that in collisionsaluminum can perform as well as conventional steel and demonstrates theability to absorb twice the crash energy per pound of mild steel, havinggood buckling and energy absorption characteristics.

In body-in-white structures, joining methods have traditionally reliedon resistance-spot welding (e.g., in steel structures). In the case ofaluminum intensive vehicles and other mixed metal joining applications,self-piercing rivet (SPR) technology prevails. One advantage of SPRtechnology is that it is a high production volume assembly process.Further, it is compatible with an adhesive, where both methods can beused in conjunction.

The challenge often faced with SPR, however, is that the substratematerial may be difficult to pierce. This can result in rivet fractureor buckling, thereby compromising joint integrity. Moreover, uponriveting the substrate material may accumulate damage which isundesirable for durability resistance. One example of this is fiberdelamination in composite materials. Lastly, corrosion concerns can beintroduced when a large galvanic potential exists between the rivetmaterial versus the substrate material. This can degrade the jointintegrity with time and exposure to ambient environmental conditions.

As in so many areas of vehicle technology there is always room forimprovement related to the mechanical fastening of the materials throughself-pierce riveting.

SUMMARY OF THE INVENTION

The disclosed inventive concept overcomes the problems associated withknown systems and methods for self-pierce riveting materials together,of which some may be hard materials. The disclosed inventive conceptprovides a solution to these types of applications by providing aclearance hole formed in either the upper layer in the case of twolayers or the middle layer in the case of three layers for the rivet.The disclosed inventive concept also has application where more thanthree layers of material are to be self-pierce riveted. By having one ormore clearance holes formed the deformation of the substrate and therivet is avoided, thus overcoming the challenges faced by the prior artapproaches to riveting materials together.

The disclosed inventive concept also applies to joints where fiberdelamination must be minimized, such as carbon-fiber compositematerials. A clearance hole is placed into the composite layer, thusavoiding substrate damage during the self-pierce riveting process.

The disclosed inventive concept thus overcomes the challenges faced inindustry during assembly processes where different materials are beingjoined. Thus an important advantage of the disclosed inventive conceptis that it enables greater application of SPR joining, particularly indifficult stacks. Without this solution, the use of mixed materials andultra-high strength and low ductility materials must be reduced, as noother low cost, automated joining solution exists.

The above advantages and other advantages and features will be readilyapparent from the following detailed description of the preferredembodiments when taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this invention, reference shouldnow be made to the embodiments illustrated in greater detail in theaccompanying drawings and described below by way of examples of theinvention wherein:

FIG. 1A is a schematic illustration of the first step of a self-piercingrivet process according to the prior art in which the blankholder andthe punch are in position above the rivet prior to pressure beingapplied to the punch;

FIG. 1B is a schematic illustration of the second step of theself-piercing rivet process according to the prior art in which initialpressure has been applied to the punch;

FIG. 1C is a schematic illustration of the third step of theself-piercing rivet process according to the prior art in which therivet has pierced the upper layer and is interlocked into the lowerlayer;

FIG. 1D is a schematic illustration of the fourth step of theself-piercing rivet process according to the prior art in which therivet process has been completed and the punch and blankholder have beenremoved;

FIG. 2 is a schematic view of an arrangement according to a firstembodiment of the disclosed inventive concept where a clearance hole hasbeen formed in the upper layer of a stack-up having two layers ofmaterial;

FIG. 3 is a schematic view of an arrangement according to a secondembodiment of the disclosed inventive concept where a clearance hole hasbeen formed in the middle layer of a stack-up having three layers ofmaterial;

FIG. 4 is a schematic view of an arrangement according to a thirdembodiment of the disclosed inventive concept where a clearance hole hasbeen formed in the top layer of a stack-up having four layers ofmaterial;

FIG. 5 is a schematic view of an arrangement according to a fourthembodiment of the disclosed inventive concept where a clearance hole hasbeen formed in the top layer and in the second layer of a stack-uphaving four layers of material;

FIG. 6 is a schematic view of an arrangement according to a fifthembodiment of the disclosed inventive concept where a clearance hole hasbeen formed in the top layer and in the third layer of a stack-up havingfour layers of material; and

FIG. 7 is a schematic view of an arrangement according to a sixthembodiment of the disclosed inventive concept where a clearance hole hasbeen formed in the second layer and in the third layer of a stack-uphaving four layers of material.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In the following figures, the same reference numerals will be used torefer to the same components. In the following description, variousoperating parameters and components are described for differentconstructed embodiments. These specific parameters and components areincluded as examples and are not meant to be limiting.

The disclosed inventive concept may find use in any number ofapplications where plural layers of the same or dissimilar materials arebeing attached. Accordingly, the disclosed inventive concept may be usedin the production of automotive vehicles and trucks.

The use of self-piercing rivets in the assembly of plural components isa known technique as illustrated in FIGS. 1A through 1D. These figuresschematically show steps involved in the self-piercing rivet process. Asthe rivet is inserted into the stack, the material deforms into the dieand the resultant form is called a “button.”

As illustrated in FIG. 1A, the first step of a self-piercing rivetprocess according to the prior art is illustrated. A first layer 10 isshown in position over a second layer 12. A rivet 14 is illustrated inposition over the first layer 10. A punch 16 and a blankholder 18 areillustrated in position with the rivet 14 prior to pressure beingapplied to the punch 16. A die 20 is in position beneath the secondlayer 12.

In FIG. 1B, the second step of the self-piercing rivet process accordingto the prior art is illustrated. In this step, initial pressure has beenapplied to the punch 16 and the rivet 14 is shown beginning to deformthe first layer 10 and the second layer 12.

In FIG. 1C, the third step of the self-piercing rivet process accordingto the prior art is illustrated. In this step, the punch 16 has beenfully inserted through the blankholder 18 such that the rivet 14 piercedthe first layer 10 and forms the second layer 12.

In FIG. 1D, the fourth step of the self-piercing rivet process accordingto the prior art is illustrated. In this step, the rivet 14 is shownfully inserted through the first layer 10 and a button is formed in thesecond layer 12. The punch 16 and the blankholder 18 have been moved outof contact with the first layer 10.

The disclosed inventive concept may be used with any combination of twoor more layers of material as shown in FIGS. 2 and 3. In FIG. 2, twolayers are illustrated as being riveted. In FIG. 3, three layers areillustrated as being riveted. It is possible that more than three layersof material may be riveted according to the disclosed inventive concept.

Referring to FIG. 2, a schematic view of an assembled joint according toa first embodiment of the disclosed inventive concept, generallyillustrated as 30, is shown. The joint 30 includes a material stack-upthat is defined by a first layer 32 positioned over a second layer 34. Aclearance hole 36 is formed in the first layer 32. The first layer 32 isa hard material that, if the clearance hole 36 is not formed beforeriveting, it may result in a poor mechanical connection because of rivetfracture or buckling, thereby compromising joint integrity. Such hardmaterial might include without limitation a hard steel such as carbonsteel grade (DP800).

However, the disclosed inventive concept is not limited to the formationof a clearance hole in a metal. As a non-limiting example, the disclosedinventive concept also applies to joints where fiber delamination mustbe minimized, such as carbon-fiber composite materials. In such a casethe clearance hole is placed into the composite layer, thus avoidingsubstrate damage during riveting.

With the clearance hole 36 formed in the first layer 32 and the firstlayer 32 placed on the second layer 34, a rivet 38 is inserted throughthe clearance hole 36 during joining and interlocks into the secondlayer 34 which is composed of an unspecified sheet of material that maybe the same as or different from the material of the first layer 32. Therivet 38 includes a rivet head 40 that provides a clamping force, a body42, and a tail 44. At the intersection of the head 40 and the body 42, asloped surface 47 is formed therein. The body 42 includes a bore 45formed therein to define a tubular or semi-tubular rivet. The bore 45extends from the tail 44 and terminates at the head 40.

According to the system of the disclosed inventive concept, the rivet 38does not pierce the first layer 32 having the clearance hole 36 andthereby avoids compromising the rivet 38. The clamping force of thejoint 30 is provided by the rivet head 40 of the rivet 38 which extendsbeyond the diameter of the clearance hole 36. However, the slopedsurface 47 causes the head 40 to be at least partially rooted orembedded within the first layer 32. The piercing action results in aportion of the second layer 34 being captured within the bore 45 of thebody 42 of the rivet 38. Additionally, the tail 44 interlocks with thesecond layer 34 due to the bore 45 permitting the tail 44 to flareoutwardly and into the second layer 34.

The disclosed inventive concept may apply to material stack-ups greaterthan two layers as illustrated in FIG. 3. This figure illustrates aschematic view of an assembled joint according to a second embodiment ofthe disclosed inventive concept, generally illustrated as 50. The joint50 includes a material stack-up that is defined by a first layer 52, asecond or middle layer 54, and a third layer 56. Thus the second ormiddle layer 54 is sandwiched between the first layer 52 and the thirdlayer 56. However, it is to be understood that more than three layers ofmaterial may be included in the material stack-up being riveted asillustrated in FIGS. 4 through 7 and as discussed in conjunctiontherewith.

A clearance hole 58 is formed in the second or middle layer 54 beforethe first layer 52 and the third layer 56 are placed in position on thesecond or middle layer 54. With the clearance hole 58 formed in thesecond or middle layer 54 and the first layer 52 and the third layer 56placed on the second or middle layer 54, a rivet 60 is inserted throughthe clearance hole 58 during joining. The rivet 60 includes a rivet head62, a body 64, and a tail 66 that interlocks with the third layer 56upon joining. At the intersection of the head 62 and the body 64, asloped surface 67 is formed therein. The body 64 includes a bore 65formed therein to define a tubular or semi-tubular rivet. The bore 65extends from the tail 66 and terminates at the head 62.

The first layer 52, the second or middle layer 54 and the third layer 56may be any of a variety of materials including metals (such as steel or,more particularly, the above-mentioned carbon steel grade [DP800]) orcarbon-fiber composites. However, it is generally understood that thesecond or middle layer 54 is a material difficult to pierce with a rivetwithout fracturing the rivet or causing damage to the substratematerial. The materials may be the same or may be different from eachother.

According to the system of the disclosed inventive concept illustratedin FIG. 3, the rivet 60 does pierce the first layer 52 and forms abutton in the third layer 56 but does not pierce the second or middlelayer 54 having the clearance hole 58 and thereby avoids compromisingthe rivet 60. The clamping force of the joint 50 is provided by therivet head 62 of the rivet 60 that extends beyond the diameter of theclearance hole 58. The piercing action results in a portion of the firstlayer 52 being captured within the bore of the body 64 of the rivet 60.

When the clearance hole 58 is in one of the middle sheets, corrosionconcerns are mitigated due to the lack of contact between the rivetmaterial (often high strength boron steel, e.g. 10B37) and the substrate(e.g., magnesium alloys, including AM60), as the rivet 60 passes througha clearance hole 58.

As a further variation of the disclosed inventive concept, materialstack-ups greater than three layers may benefit from the system andmethod of using a rivet as a mechanical fastener disclosed herein.Particularly, and referring generally to FIGS. 4 through 7, a materialstack up of four layers is illustrated. However, it is to be understoodthat material stack-ups greater than four layers may also be formedusing a rivet in conjunction with a clearance hole as provided herein.

With respect to FIG. 4, a schematic view of an assembled joint accordingto a third embodiment of the disclosed inventive concept is shown and isgenerally illustrated as 70. The joint 70 includes a material stack-upthat is defined by a first layer 72, a second layer 74, a third layer76, and a fourth layer 78. Thus the second layer 74 and the third layer76 are sandwiched between the first layer 72 and the fourth layer 78.

The first layer 72, the second layer 74, the third layer 76 and thefourth layer 78 may be any of a variety of materials including metals(such as steel or, more particularly, the above-mentioned carbon steelgrade [DP800]) or carbon-fiber composites. The materials may be the sameor may be different from each other.

A clearance hole 80 is formed in the first layer 72 before the layers72, 74, 76 and 78 are sandwiched together. With the clearance hole 80formed in the first layer 72 and the first layer 72 placed on the secondlayer 74, the third layer 76 and the fourth layer 78, a rivet 82 isinserted through the clearance hole 80 during joining. The rivet 82includes a rivet head 84 that provides a clamping force. The rivet 82further includes a body 86 and a tail 88. At the intersection of thehead 84 and the body 86, a sloped surface 87 is formed therein. The body86 includes a bore 85 formed therein to define a tubular or semi-tubularrivet. The bore 85 extends from the tail 88 and terminates at the head84.

Upon insertion, the rivet 82 pierces the second layer 74 and the thirdlayer 76. The tail 88 of the rivet 82 interlocks with the fourth layer78. The piercing action results in a portion of the second layer 74 anda portion of the third layer 76 being captured within the bore of thebody 86 of the rivet 82.

With respect to FIG. 5, a schematic view of an assembled joint accordingto a fourth embodiment of the disclosed inventive concept is shown andis generally illustrated as 90. The joint 90 includes a materialstack-up that is defined by a first layer 92, a second layer 94, a thirdlayer 96, and a fourth layer 98. Thus the second layer 94 and the thirdlayer 96 are sandwiched between the first layer 92 and the fourth layer98.

The first layer 92, the second layer 94, the third layer 96 and thefourth layer 98 may be any of a variety of materials including metals(such as steel or, more particularly, the above-mentioned carbon steelgrade [DP800]) or carbon-fiber composites. The materials may be the sameor may be different from each other.

A first clearance hole 100 is formed in the first layer 92 and a secondclearance hole 102 is formed in the second layer 94. The first clearancehole 100 and the second clearance hole 102 are formed in the layers 92and 94 respectively before the layers 92, 94, 96 and 98 are sandwichedtogether. With the first clearance hole 100 formed in the first layer92, with the second clearance hole 102 formed in the second layer 94,and with the layers 92, 94, 96 and 98 assembled as a stack, a rivet 104is inserted through the first clearance hole 100 and the secondclearance hole 102 during joining. The rivet 104 includes a rivet head106 that provides a clamping force. The rivet 104 further includes abody 108 and a tail 110. At the intersection of the head 106 and thebody 108, a sloped surface 107 is formed therein. The body 108 includesa bore 105 formed therein to define a tubular or semi-tubular rivet. Thebore 105 extends from the tail 110 and terminates at the head 106.

Upon insertion, the rivet 104 pierces the third layer 96. The tail 110of the rivet 104 interlocks with the fourth layer 98. The piercingaction results in a portion of the third layer 96 being captured withinthe bore of the body 108 of the rivet 104.

With respect to FIG. 6, a schematic view of an assembled joint accordingto a fifth embodiment of the disclosed inventive concept is shown and isgenerally illustrated as 120. The joint 120 includes a material stack-upthat is defined by a first layer 122, a second layer 124, a third layer126, and a fourth layer 128. Thus the second layer 124 and the thirdlayer 126 are sandwiched between the first layer 122 and the fourthlayer 128.

The first layer 122, the second layer 124, the third layer 126 and thefourth layer 128 may be any of a variety of materials including metals(such as steel or, more particularly, the above-mentioned carbon steelgrade [DP800]) or carbon-fiber composites. The materials may be the sameor may be different from each other.

A first clearance hole 130 is formed in the first layer 122 and a secondclearance hole 132 is formed in the third layer 126. The first clearancehole 130 and the second clearance hole 132 are formed in the layers 122and 126 respectively before the layers 122, 124, 126 and 128 aresandwiched together. With the first clearance hole 130 formed in thefirst layer 122, with the second clearance hole 132 formed in the thirdlayer 124, and with the layers 122, 124, 126 and 128 assembled as astack, a rivet 134 is inserted through the first clearance hole 130 andthe second clearance hole 132 during joining. The rivet 134 includes arivet head 136 that provides a clamping force. The rivet 134 furtherincludes a body 138 and a tail 140. At the intersection of the head 136and the body 138, a sloped surface 137 is formed therein. The body 138includes a bore 135 formed therein to define a tubular or semi-tubularrivet. The bore 135 extends from the tail 140 and terminates at the head136.

Upon insertion, the rivet 134 pierces the second layer 124. The tail 140of the rivet 134 interlocks with the fourth layer 128. The piercingaction results in a portion of the second layer 96 being captured withinthe bore of the body 138 of the rivet 134.

With respect to FIG. 7, a schematic view of an assembled joint accordingto a sixth embodiment of the disclosed inventive concept is shown and isgenerally illustrated as 150. The joint 150 includes a material stack-upthat is defined by a first layer 152, a second layer 154, a third layer156, and a fourth layer 158. Thus the second layer 154 and the thirdlayer 156 are sandwiched between the first layer 152 and the fourthlayer 158.

The first layer 152, the second layer 154, the third layer 156 and thefourth layer 158 may be any of a variety of materials including metals(such as steel or, more particularly, the above-mentioned carbon steelgrade [DP800]) or carbon-fiber composites. The materials may be the sameor may be different from each other.

A first clearance hole 160 is formed in the second layer 154 and asecond clearance hole 162 is formed in the third layer 156. The firstclearance hole 160 and the second clearance hole 162 are formed in thelayers 154 and 156 respectively before the layers 152, 154, 156 and 158are sandwiched together. With the first clearance hole 160 formed in thesecond layer 154, with the second clearance hole 162 formed in the thirdlayer 156, and with the layers 152, 154, 156 and 158 assembled as astack, a rivet 164 is inserted through the first clearance hole 160 andthe second clearance hole 162 during joining. The rivet 164 includes arivet head 166 that provides a clamping force. The rivet 164 furtherincludes a body 168 and a tail 170. At the intersection of the head 166and the body 168, a sloped surface 167 is formed therein. The body 168includes a bore 165 formed therein to define a tubular or semi-tubularrivet. The bore 165 extends from the tail 170 and terminates at the head166.

Upon insertion, the rivet 164 pierces the first layer 152. The tail 170of the rivet 164 interlocks with the fourth layer 158. The piercingaction results in a portion of the first layer 152 being captured withinbore of the body 168 of the rivet 164.

One of the advantages of the disclosed inventive concept is that itenables greater application of self-piercing rivet joining, particularlyin difficult stacks. Without this solution, the use of mixed materialsand ultra-high strength and low ductility materials must be reduced, asno other low cost, automated joining solution exists.

For at least the above reasons the disclosed invention as set forthabove overcomes the challenges faced by known methods for rivetingmultiple layers of material by forming a clearance hole in at least oneof the layers of material. However, one skilled in the art will readilyrecognize from such discussion, and from the accompanying drawings andclaims that various changes, modifications and variations can be madetherein without departing from the true spirit and fair scope of theinvention as defined by the following claims.

1-20. (canceled)
 21. A system for attaching layers of material togethercomprising: a self-piercing rivet having a head, body and tail; aplurality of layers, including: a top layer; a bottom layer free of aclearance hole and into which said self-piercing rivet is at leastpartially inserted; two or more middle layers provided between the toplayer and bottom layer; and a clearance hole through which saidself-piercing rivet passes during assembly in one of the: i) top layer;ii) the top layer and an uppermost layer of the two or more middlelayers; iii) the top layer and a lowermost layer of the two or moremiddle layers; and iii) two or more of the two or more middle layers,wherein each clearance hole is configured to provide a hollow clearancespace between the self-piercing rivet and each of the plurality oflayers in which a clearance hole is provided after the plurality oflayers are attached together by said self-piercing rivet with a portionof a layer of the plurality of layers in which a clearance hole is notprovided being captured within the body of the rivet as the rivetpierces such layer.
 22. A system for attaching layers of materialtogether according to claim 21, wherein a clearance hole is onlyprovided in one of the plurality of layers.
 23. A system for attachinglayers of material together according to claim 22, wherein the clearancehole is provided in the top layer.
 24. A system for attaching layers ofmaterial together according to claim 21, wherein there are clearanceholes provided in two of the plurality of layers.
 25. A system forattaching layers of material together according to claim 24, wherein theclearance holes are provided in adjacent ones of the plurality oflayers.
 26. A system for attaching layers of material together accordingto claim 25, wherein the clearance holes are provided in the top and anuppermost middle layer.
 27. A system for attaching layers of materialtogether according to claim 25, wherein the clearance holes are providedin the middle layers.
 28. A system for attaching layers of materialtogether according to claim 24, wherein the clearance holes are providedin non-adjacent ones of the plurality of layers.
 29. A system forattaching layers of material together according to claim 28, wherein theclearance holes are provided in top and a lowermost middle layer.
 30. Asystem for attaching layers of material together according to claim 21,wherein portions of one of the plurality of layers are captured withinthe body of the rivet.
 31. A system for attaching layers of materialtogether according to claim 30, wherein portions of the top layer iscaptured within the body of the rivet.
 32. A system for attaching layersof material together according to claim 30, wherein portions of anuppermost middle layer is captured within the body of the rivet.
 33. Asystem for attaching layers of material together according to claim 30,wherein portions of a lowermost middle layer is captured within the bodyof the rivet.
 34. A system for attaching layers of material togetheraccording to claim 21, wherein portions of two of the plurality oflayers are captured within the body of the rivet.
 35. A system forattaching layers of material together according to claim 34, whereinportion of each of the two or more middle layers are captured within thebody of the rivet.
 36. A system for attaching layers of materialtogether according to claim 22, wherein the layer having the clearancehole formed therein is formed from one of steel, carbon-fiber or amagnesium alloy.
 37. A system for attaching layers of material togetheraccording to claim 24, wherein the two layers having the clearance holeformed therein are formed from one of steel, carbon-fiber or a magnesiumalloy.